A wide variety of microchips use caps to protect their interior components. For example, micro-electromechanical systems (“MEMS devices”) often have a cap to protect their fragile microstructure. Many MEMS devices typically have a glass seal to bond the silicon die caps to the underlying MEMS chip. Such a seal, which can be hermetic, may have widths on the order of about 150 to 400 microns. Undesirably, this seal footprint increases die size, especially when there is little or no support circuitry on the die. As a consequence, fewer dies/microchips can be formed from individual wafers, thus increasing per-unit fabrication costs.
Glass also can introduce contaminants and electrically isolate the cap from the die. Although the latter problem can be accommodated by wirebonding to the cap, such a solution increases package height. One alternative to using a glass seal involves use of a thermocompression bonded metal. Undesirably, however, thermocompression bonding generally requires wafers to have minimal topography due to the high pressures required in such processes.